Loss of protective ozone in the stratosphere in recent years has resulted in increased penetration of harmful ultraviolet radiation to the earth's surface. Such losses have resulted in the creation of a large "ozone hole" in the Antarctic. Generation of a similar ozone hole or holes in the Arctic have also been projected.
Anticipated health effects in regions beneath an ozone hole are expected to include an increase in cataracts, skin cancer and immune system damage in humans, along with similar effects in animals. It is possible that the growth of phytoplankton in the oceans, as well as crop yields on land, may be adversely affected.
Ozone destruction has been accelerated by increased amounts of Cl and ClO radicals originating from man-made chlorofluorocarbons (CFCs) by reactions such as: EQU CF.sub.2 Cl.sub.2 +(hV) (ultraviolet radiation).fwdarw.CF.sub.2 Cl+Cl
followed by reactions: EQU Cl+O.sub.3 .fwdarw.ClO+O.sub.2 EQU .DELTA.F.sub.298 =-40.8 Kcal/mol EQU .DELTA.H.sub.298 =-38.8 Kcal/mol
and: EQU ClO+O(.sup.3 P.sub.2).fwdarw.Cl+O.sub.2 EQU .DELTA.F.sub.298 =-53.6 Kcal/mol EQU .DELTA.H.sub.298 =-54.8 Kcal/mol
with the overall result: EQU O.sub.3 +O.fwdarw.2O.sub.2 EQU .DELTA.F.sub.298 =-99.4 Kcal/mol EQU .DELTA.H.sub.298 =-93.7 Kcal/mol
Another pathway to ozone destruction reported by Molina is the heterogeneous process occurring when polar stratospheric ice clouds (PSCs) as subjected to UV irradiation as illustrated by the reaction: ##STR1## in which photochemically active molecular chlorine is liberated from the labile chlorine nitrate reservoir: EQU Cl.sub.2 +(hV).fwdarw.2Cl
The Cl radical reaction with ambient ozone produces a ClO radical and destroys ozone in the process. EQU Cl+O.sub.3 .fwdarw.ClO+O.sub.2 EQU .DELTA.F.sub.298 =-40.8 Kcal/mol
ClO then combines with ambient NO.sub.2 to reform the ClONO.sub.2 sink on ice particles. The process can continue to repeat itself with additional ambient HCl. ##STR2##
A further heterogeneous catalytic process for ozone destruction may involve sulfate bearing aerosols resulting from fossil fuel combustion, automotive exhaust, or from volcanic activity. It is known, for example, that ozone is decomposed when shaken with powdered glass, or catalytically contacted with metallic silver, platinum, manganese dioxide, lead dioxide, silver, cobalt or iron oxides. Such particulates are released from coal burning power plants and from automobile exhaust using lead or manganese additives in gasoline.
Volcanic action sometimes results in the injection into the stratosphere of magma containing iron or manganese silicates. Such eruptions are often accompanied by a release of sulfur dioxide. When SO.sub.2 is eventually oxidized to SO.sub.3 (sulfur trioxide) and then hydrolizes to sulfuric acid, it may react to produce the ozone destroying catalysts Fe+2 and Mn+2.
For example: EQU MnSiO.sub.3 +H.sub.2 SO.sub.4 (aq).fwdarw.MnSO.sub.4 (aq)+H.sub.2 SiO.sub.3 EQU .DELTA.F.sub.298 =-19.2 Kcal/mol EQU H.sub.2 O+MnSO.sub.4 (aq)+O.sub.3 .fwdarw.MnO.sub.2 +H.sub.2 SO.sub.4 (aq)+O.sub.2 EQU .DELTA.F.sub.298 =-38.9 Kcal/mol
In summary, it is known that man-made chlorinated organics greatly exceed naturally occurring chlorinated compounds. Under stratospheric ultraviolet irradiation, these compounds, mostly CFCs (chlorofluorocarbons) slowly break up--yielding atomic chlorine fragments, with each chlorine radical being capable of destroying many ozone molecules before chain termination. It has been estimated that the retention times for these compounds in the stratosphere may range up to 100 years with each radical destroying up to 100,000 ozone molecules. Even with immediate cessation of CFC production, the protective ozone layer now in the stratosphere is expected to continue to decrease, allowing more short wavelength ultraviolet radiation to pass to earth where it can damage plant and animal life.
If the current destruction of ozone is not arrested, upper stratospheric losses of 25% may be encountered in the next 75 years, leading to upper stratospheric cooling of as much as 5.degree. C. This could significantly alter stratospheric circulation patterns. Furthermore, the ozone levels in the troposphere would be expected to increase as a consequence, leading to increased surface heating, since ozone acts as a greenhouse gas in the troposphere.
In light of the harm caused by Cl and ClO radicals, it would be beneficial to develop a method of scavenging Cl and ClO radicals and especially the reservoir compounds from which they are continually derived, as well as other ozone destroying compounds, from the stratosphere. It would also be desirable to provide a method for arresting the destruction of protective ozone which does not have an undue adverse environmental impact.